Drive train

ABSTRACT

A drive train including an internal combustion engine having a predefined number of cylinders, and operable in a first engine operating state in which all cylinders are in operation, and a second operating state in which some of the cylinders are not in operation. The drive train has a torsional-vibration damping system with at least one torsional-vibration damper and at least one centrifugal-force pendulum. In order to improve the torsional-vibration behavior of the drive train, a centrifugal-force pendulum and optionally a torsional-vibration damper are adapted to control torsional-vibration behavior of the engine in one operating state, and a torsional-vibration damper and optionally a second centrifugal-force pendulum are adapted to control the torsional-vibration behavior of the engine in the other engine operating state.

CROSS-REFERENCE TO RELATED APPLICATION

This application is the U.S. national phase application under 35 U.S.C.§371 of International Application Serial No. PCT/DE2012/001129, havingan international filing date of 26 Nov. 2012, and designating the UnitedStates, the entire contents of which are hereby incorporated byreference to the same extent as if fully rewritten.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive train including an internalcombustion engine with a predefined number of cylinders, with a firstoperating state in which all cylinders are in operation, a secondoperating state in which some of the cylinders are switched off, andincluding a torsional-vibration damping system with at least onetorsional-vibration damper and at least one centrifugal pendulum.

2. Description of the Related Art

Drive trains of this general type are typically used in motor vehicles.They include an internal combustion engine, a transmission, and a drivefor driving the motor vehicle. Torsional-vibration damping systems thatinclude one or more torsional-vibration dampers, for instance, are knownin the art for isolating and damping torsional vibration of the internalcombustion engine. The torsional-vibration dampers are preferablyarranged on the crankshaft, or on a transmission input shaft of thetransmission, and can be divided flywheels, torsional-vibration dampersin clutch discs of a friction clutch arranged between the crankshaft andthe transmission input shaft and the like, and are known, for example,from the documents DE 37 03 123 A1 and DE 34 42 705 A1. Furthermorecentrifugal pendulums have become known in the art as torsionalvibration dampers, for example from the document DE 10 2010 005 599 A1.These centrifugal pendulums form a rotary-speed adaptivetorsional-vibration damper by means of pendulum masses that may pivot toa limited extent relative to a pendulum flange received with thecrankshaft or transmission input shaft. Moreover, combinations ofcentrifugal pendulums and the aforementioned torsional-vibration dampersare known, for example, from WO 2011/110153 A1, DE 10 2010 018 941 A1,and DE 10 2010 022 252 A1. The torsional-vibration damping system isadapted to the torsional-vibration behavior of the internal combustionengine, for example to the vibration order thereof. For four-strokeengines with four cylinders the vibration orders equal two and forfour-stroke engines with two cylinders, the vibration orders equal one,for example.

DE 100 36 720 A1, for instance, discloses an internal combustion enginewherein a predefined number of cylinders can be switched off to saveenergy in driving situations that have low load requirements, and can beswitched back on when a corresponding torque is required. The result isan internal combustion engine with two modes of operation in one drivetrain with different vibration orders, and thus differenttorsional-vibration behavior.

An object of the present invention is to provide a drive train thatachieves an improved torsional-vibration behavior in both operatingstates of the internal combustion engine as a result of an adaptabletorsional-vibration system.

SUMMARY OF THE INVENTION

The object is attained by a drive train including an internal combustionengine with a predefined number of cylinders, with a first operatingstate in which all cylinders are in operation, and a second operatingstate in which some of the cylinders are switched off. The drive trainfurther includes a torsional-vibration damping system with at least onetorsional-vibration damper and at least one centrifugal pendulum,wherein a centrifugal pendulum and optionally a torsional-vibrationdamper are adapted to the torsional-vibration behavior of one operatingstate, and a torsional-vibration damper and optionally a secondcentrifugal pendulum are adapted to the torsional-vibration behavior ofthe other operating state. The use of multiple components of thetorsional-vibration damping system in the form of at least onecentrifugal pendulum and at least one torsional-vibration damper canimprove the torsional-vibration behavior of the two operating states ofthe internal combustion engine selectively for each operating state. Oneor more components can be associated with each operating state.

One or more torsional-vibration dampers can be embodied as a dividedflywheel with a spring device that is arranged between a primaryinertial mass associated with the crankshaft, and a secondary inertialmass associated with a transmission input shaft of a transmission, andis arranged to be effective in the circumferential direction and has atleast one damper stage. One or more torsional-vibration dampers can beembodied as a torsional-vibration damper with at least one damper stagein a clutch disc of a friction clutch that is arranged between theinternal combustion engine and a transmission in the drive train, or asa similar system. If multiple damper stages are provided in atorsional-vibration damper, one damper stage can be associated with oneoperating state and the other damper stage can be associated with theother operating state and can be adapted to improve thetorsional-vibration behavior thereof. For this purpose, the stiffnessesof the damper stages in the circumferential direction and rotationangles between the input and output parts of the torsional-vibrationdampers are adapted in a corresponding way. In this context, higherdegrees of stiffness are particularly advantageous for the damping andtransmission of higher torques at comparatively small rotation angles,and lower degrees of stiffness are particularly advantageous for thecompensation of vibrations at lower torques and larger rotation angles.The damper stages of lower stiffness are preferably by-passed at highertorques to protect them. The spring device can be formed of arc springsand/or coil springs. It is preferred that in one damper stage of adivided flywheel arc springs be provided, and otherwise helicalcompression springs be provided.

One or more centrifugal pendulums can be arranged at different locationsof the drive train. It can be advantageous to adapt a single centrifugalpendulum to different orders of vibration, for example by providingpendulum masses of different vibration behaviors in that the pendulummasses include masses and/or vibration angles adapted to a respectiveorder of vibration. A respective centrifugal pendulum can be arranged onthe primary or secondary inertial mass of a torsional-vibration damperand/or on a torsional-vibration damper in a clutch disc, or on afriction clutch arranged between the crankshaft and the transmissioninput shaft in the drive train.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below based on theexemplary embodiments shown in FIGS. 1 to 14, wherein

FIG. 1 is a diagrammatic representation of a section of a drive trainthat includes a torsional-vibration damping system with twotorsional-vibration dampers and a secondary-side centrifugal pendulum;

FIG. 2 is a characteristic torque curve of the drive train shown in FIG.1;

FIG. 3 is a diagrammatic representation of a section of a drive trainthat includes a torsional-vibration damping system with twotorsional-vibration dampers and a primary-side centrifugal pendulum;

FIG. 4 is a characteristic torque curve of the drive train shown in FIG.3;

FIG. 5 is a diagrammatic representation of a section of a drive trainsimilar to the drive train shown in FIG. 1, and including atorsional-vibration damping system with two torsional-vibration damperswith a modified characteristic curve and a secondary-side centrifugalpendulum;

FIG. 6 is a characteristic torque curve of the drive train shown in FIG.5;

FIG. 7 is a diagrammatic representation of a section of a drive trainsimilar to the drive train shown in FIG. 1 and including atorsional-vibration damping system with two torsional-vibration damperswith a modified characteristic curve and a primary-side centrifugalpendulum;

FIG. 8 is a characteristic torque curve of the drive train shown in FIG.7;

FIG. 9 is a diagrammatic representation of a section of a drive trainthat includes a torsional-vibration damping system with twotorsional-vibration dampers and a centrifugal pendulum arranged on atorsional-vibration damper of a clutch disc;

FIG. 10 is a characteristic torque curve of the drive train shown inFIG. 9;

FIG. 11 is a diagrammatic representation of a section of a drive trainthat includes a torsional-vibration damping system with twotorsional-vibration dampers and a respective centrifugal pendulum on atorsional-vibration damper;

FIG. 12 is a characteristic torque curve of the drive train shown inFIG. 11;

FIG. 13 is a diagrammatic representation of a section of a drive trainsimilar to the drive train shown in FIG. 11 and including atorsional-vibration damping system with two torsional-vibration dampersand a respective centrifugal pendulum arranged on a torsional-vibrationdamper; and

FIG. 14 is a characteristic torque curve of the drive train shown inFIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a diagrammatic representation of a drive train 10 thatincludes an internal combustion engine 11 selectively operable in twooperating states with four or two cylinders. Drive train 10 includes atorsional-vibration damping system 12, as well as a unit 14 thatdiagrammatically indicates a transmission and a vehicle body and iscoupled in a torsionally flexible way by a torsional flexibility element13. The torsional-vibration damping system 12 is formed by a firsttorsional-vibration damper 15, embodied as a divided flywheel 16 with aprimary inertial mass 17 and a secondary inertial mass 18, by adownstream second torsional-vibration damper 19 integrated in a clutchdisc of a friction clutch, and by a primary-side centrifugal pendulum20. A spring device having spring rates c1 and c2 is associated with thefirst two-stage torsional-vibration damper 15. To improve thetorsional-vibration behavior of the first operating state of theinternal combustion engine 11 with all cylinders (four in theillustrated embodiment) in operation, the centrifugal pendulum 20 isadapted to the order of vibration one. Furthermore, the second damperstage having the spring rate c2 of higher stiffness is adapted to be inoperation in the second operating state.

Due to the fact that cylinders are switched off, a lower torque isapplied to the torsional-vibration damping system 12 in the secondoperating state, so that the torsional-vibration behavior can beimproved by means of the first, softer damper stage having the springrate c1. The second torsional-vibration damper 19 can selectively oroverall be associated with one operating state.

FIG. 2 illustrates a graph 21 in which the torque M of the firsttorsional-vibration damper 15 of FIG. 1 is plotted above the angle ofrotation φ of the inertial masses 17, 18 in a characteristic torquecurve 22. Since in the second operating state of the internal combustionengine 11 the maximum switch-off torque M_(z) with switched-offcylinders is correspondingly reduced, a sufficient damping effect can beachieved by the damper stage that has the spring rate c1, whereas whenthe cylinders are switched on in the second operating state, when thetorque is above the switch-off torque M_(z), the second damper stagethat has the spring rate c2 and the centrifugal pendulum 20, whoseeffect is not visible here, are effective as a damper that is adaptiveto the rotary speed.

FIG. 3 illustrates a drive train 110 different from the drive train 10of FIG. 1 in that the torsional-vibration damping system 112 with thefirst torsional-vibration damper 115 and the second torsional-vibrationdamper 119 includes the primary-side centrifugal pendulum 120 arrangedon the inertial mass 117. The centrifugal pendulum 120 is adapted to thevibration order of the internal combustion engine when all cylinders arein operation, i.e., to the first operating state, which in the case of afour-cylinder engine according to the 4-stroke principle is vibrationorder two. As the primary-side inertial mass 117 is increased by thecentrifugal pendulum 120, the second operating state also benefits dueto a more efficient damping, although the centrifugal pendulum 120 isnot adapted to the order of vibration thereof.

FIG. 4 illustrates a graph 121 resulting from the torsional-vibrationdamper 115 of FIG. 3, with characteristic torque curve 122 and with thetwo spring rates c1, c2 associatable with the two damper stages in a waycorresponding to graph 21 of FIG. 2.

FIG. 5 illustrates a drive train 210, which is similar to the drivetrain 10 of FIG. 1. Drive train 210 includes a torsional-vibrationdamping system 212 with two torsional-vibration dampers 215, 219 and asecondary-side centrifugal pendulum 220 arranged on the secondaryinertial mass 218. As it is apparent from the graph 221 of FIG. 6illustrating the characteristic torque curve 222, in contrast to thesecond damper stage with the spring rate c2 of the firsttorsional-vibration damper 15 of FIG. 1, the second damper stage withthe spring rate c2 of the first torsional-vibration damper 215 iseffective over a wide torque range in both operating states of theinternal combustion engine. The first damper stage can damptorsional-vibration during the idle phase, or it can be dispensed withto simplify the first torsional-vibration damper 215.

In a corresponding way, FIG. 7 illustrates a drive train 310 similar tothe drive trains 110, 210 of FIGS. 3 and 5 and including a correspondingtorsional-vibration damping system 312, wherein the centrifugal pendulum320 is arranged on the primary inertial mass 317 of the firsttorsional-vibration damper 315. As it is apparent from the graph 321 ofFIG. 8 with characteristic torque curve 322, the damper stages with thespring rates c1, c2 of the first torsional-vibration damper 315 aresimilar to those of the torsional-vibration damper 215 of FIG. 5.

FIG. 9 illustrates a drive train 410 including a torsional-vibrationdamping system 412 with two torsional-vibration dampers 415, 419 and acentrifugal pendulum 424, which, in contrast to the drive trainsdescribed above, is arranged on the second torsional-vibration damper419, for example a torsional-vibration damper of a clutch disc. Thetorsional-vibration damping system improves the torsional vibration ofthe drive train 410 in that the centrifugal pendulum 424 arranged on thesecond torsional-vibration damper 419, and a second damper stage of highstiffness with the spring rate c2, are adapted to thetorsional-vibration behavior of the first operating state, i.e., on theorder of vibration two of a four-cylinder engine in accordance with the4-stroke principle. A first damper stage of low stiffness with thespring rate c1 and additionally, or alternatively, a spring device 423of the second torsional-vibration damper 419, are adapted to thetorsional-vibration behavior of the second operating state.

FIG. 10 illustrates a graph 421 with characteristic torque curve 422 ofthe torsional-vibration damping system 412 of FIG. 9. Up to the maximumswitch-off torque M_(z) in the second operating state with partiallyswitched-off cylinders of an internal combustion engine corresponding tothe internal combustion engine 11 of FIG. 1, the first damper stage ofthe first torsional-vibration damper 415 with the spring rate c1 and,additionally or alternatively, for a one-stage torsional-vibrationdamper 415, the spring device 423 with the spring rate c3 of the secondtorsional-vibration damper 419 are provided. For torques above theswitch-off torque M_(z) when all cylinders are in operation in the firstoperating state of the internal combustion engine, the second damperstage with the spring rate c2 is provided to damp thetorsional-vibrations.

FIG. 11 illustrates a drive train 510, which is similar to drive train410 and includes a torsional-vibration damping system 512. In contrastto the aforementioned drive trains, in the drive train of FIG. 11 acentrifugal pendulum 520, 524 is arranged on each of thetorsional-vibration dampers 515, 519. The centrifugal pendulum 520arranged on the secondary inertial mass 518 of the firsttorsional-vibration damper 515 is adapted to the torsional-vibrationbehavior of the first operating state, for example with torsionalvibrations of vibration order two. The centrifugal pendulum 524 arrangedon the second torsional-vibration damper 519 is adapted to thetorsional-vibration behavior of the second operating state, for examplewith torsional vibrations of vibration order one. Alternatively, thecentrifugal pendulum 520 arranged on the secondary inertial mass 518 ofthe first torsional-vibration damper 515 can be adapted to thetorsional-vibration behavior of the second operating state, and thecentrifugal pendulum 524 arranged on the second torsional-vibrationdamper 519 can be adapted to the torsional-vibration behavior of thesecond operating state.

As is apparent from graph 521 of FIG. 12 with characteristic torquecurve 522, a first spring device of low stiffness is provided fortorques up to the maximum switch-off torque M_(z) and a second springdevice of high stiffness is provided for higher torques of the internalcombustion engine. Both torsional-vibration dampers 515, 519 can beone-stage dampers, and a respective torsional-vibration damper can beassociated with each operating state and centrifugal pendulum 520, 524.Torsional-vibration damper 515 is preferably provided with a springdevice of low stiffness, for example in the form of arc springs withspring rate c1, whereas the torsional-vibration damper 519 provided in aclutch disc includes a spring device of greater stiffness with springrate c3. In contrast to the torsional-vibration damping system 512 ofthe two FIGS. 11 and 12, a clutch disc without a torsional-vibrationdamper and including only one centrifugal pendulum 524 can be provided,whereas torsional-vibration damper 515 has damper stages of differentstiffness corresponding to spring rates c1, c3 of diagram 521.

FIG. 13 illustrates a drive train 610 similar to the drive train 510 ofFIG. 11 and including a torsional-vibration system 612. Here, each ofthe two centrifugal pendulums 620, 624 is adapted to a respective degreeof vibration of an operating state. For instance, the centrifugalpendulum 624 that is arranged on the second torsional-vibration damper619 is adapted to the torsional-vibration behavior of the firstoperating state, and the centrifugal pendulum 620 that is arranged on asecondary inertial mass 618 of the first torsional-vibration damper 615is adapted to the torsional-vibration behavior of the second operatingstate. As it is apparent from the graph 621 of FIG. 14 with thecharacteristic torque line 622, the damper stages of thetorsional-vibration dampers 615, 619 are selected in such a way that aspring device of high stiffness is effective even below the maximumswitch-off torque M_(z), and only a pre-damper stage of low stiffness iseffective. In the illustrated exemplary embodiment, the damper stagethat has spring rate c1 is associated with the first torsional-vibrationdamper 615, whereas the soft damper stage that has spring rate c3 isassociated with torsional-vibration damper 619. In further embodiments,the association of the damper stages with the torsional-vibrationdampers 615, 619 can be reversed, or only one two-stagetorsional-vibration damper 615 having damper stages with spring ratesc1, c3 can be provided, with the corresponding centrifugal pendulum 620arranged on the clutch disc without torsional-vibration damper.

1: A drive train comprising: an internal combustion engine having apredefined number of cylinders and operable in a first engine operatingstate in which all the cylinders are in operation, and operable in asecond engine operating state in which some of the cylinders are not inoperation, a torsional-vibration damping system including at least onetorsional-vibration damper and at least one centrifugal pendulum,wherein at least one of a centrifugal pendulum and a torsional-vibrationdamper is adapted to a control engine torsional-vibration behaviorduring the first engine operating state, and at least one of atorsional-vibration damper and a second centrifugal pendulum is adaptedto control engine torsional-vibration behavior during the second engineoperating state. 2: The drive train in accordance with claim 1, whereina first torsional-vibration damper is a divided flywheel having at leastone damper stage, and a second torsional-vibration damper is atorsional-vibration damper in a clutch disc having at least one damperstage of a friction clutch arranged between the internal combustionengine and a transmission in the drive train. 3: The drive train inaccordance with claim 2, wherein a centrifugal pendulum is arranged onat least one of a primary inertial mass and a secondary inertial mass ofthe first torsional-vibration damper. 4: The drive train in accordancewith claim 2, wherein a centrifugal pendulum is arranged on the secondtorsional-vibration damper. 5: The drive train in accordance with claim3, wherein a centrifugal pendulum is arranged on at least one of aprimary inertial mass and a secondary inertial mass of the firsttorsional-vibration damper, and the first torsional-vibration damperoperates to control engine torsional-vibration behavior during the firstengine operating state, and the first torsional-vibration damperoperates to control engine torsional-vibration behavior during thesecond engine operating state. 6: The drive train in accordance withclaim 3, wherein the first torsional-vibration damper operates tocontrol engine torsional-vibration behavior during the first engineoperating state, and a centrifugal pendulum arranged on at least one ofa primary inertial mass and a secondary inertial mass of the firsttorsional-vibration damper, and the first torsional-vibration damperoperate to control engine torsional-vibration behavior during the secondengine operating state. 7: The drive train in accordance with claim 4,wherein the centrifugal pendulum arranged on the secondtorsional-vibration damper and a first damper stage of high stiffnessoperate to control the torsional-vibration behavior of the engine duringthe first operating state, and a second damper stage of low stiffness ofthe first torsional-vibration damper operates to control thetorsional-vibration behavior of the engine during the second engineoperating state. 8: The drive train in accordance with claim 4, whereina centrifugal pendulum arranged on a secondary inertial mass of thefirst torsional-vibration damper operates to control thetorsional-vibration behavior of the engine during the first engineoperating state, and a centrifugal pendulum arranged on the secondtorsional-vibration damper operates to control the torsional-vibrationbehavior of the engine during the second engine operating state. 9: Thedrive train in accordance with claim 8, including a damper stage of highstiffness of the first torsional-vibration damper (615) is adapted thatoperates to control the torsional-vibration behavior of the engineduring the second engine operating state. 10: The drive train inaccordance with claim 8, including a damper stage of low stiffness ofthe first torsional-vibration damper operates to control thetorsional-vibration behavior of the engine during the second engineoperating state. 11: The drive train in claim 4, wherein the centrifugalpendulum arranged on the second torsional-vibration damper (519, 619) isadapted operates to control the torsional-vibration behavior of theengine during the first operating state, and a centrifugal pendulumarranged on a secondary inertial mass of the first torsional-vibrationdamper operates to control the torsional-vibration behavior of theengine during the second engine operating state.